Current Organic Chemistry - Volume 7, Issue 1, 2003

Formation and synthetic applications of carbohydrate-iron complexes possessing C-metal bond are discussed. Some of these intermediates are stable and can be isolated and characterized. In many instances, however, the sugar carbon-iron complexes exhibit a limited stability and are directly converted into the final products without their prior isolation and characterization. Nevertheless, the presence of such complexes can be inferred from spectral data.In this review the emphasis is put on the applications of carbohydrate-iron complexes in the synthesis of a less common sugar derivatives. Thus, de novo synthesis of mycaminose, an antibiotic sugar, is described employing an intermediary amino-dienone tricarbonyliron complex. Sodium (η5-cyclopentadienyl)-dicarbonyl-iron served as a source for the CO group insertion into derivatives of methyl β-D-glucopyranoside. A general method of deoxysugar synthesis was proposed starting from monosaccharide aldehydes and anion obtained from (η5-cyclopentadienylcarbonyl- triphenylphosphine-acetyl-iron (“acetyl-iron”). In that manner several derivatives of deoxy-pentoses, - hexoses as well as a series of 6-deoxy heptoses were obtained. Reactions of acetyl- and propionyl-iron anions with hexofuranose epoxides led to the heptofuranose lactones. Also, reactions of sugar aldehydes with anion derived from “(methylthioacetyl)iron” are described.The review presents the literature from 1979 (first applications of iron complexes in carbohydrate chemistry) to 2001, inclusively, 39 references.

The monosaccharide derivatives containing the C-Sn and C-Li bonds are reviewed. Both types of these organometallics are useful intermediates in the synthesis of variety of optically pure compounds such as higher carbon sugars, C-disaccharides, carbocyclic derivatives, etc.Organometallics containing the C-Sn bond are usually stable and can be isolated in the pure form, but their reactivity is low. The tin moiety in such compounds can be replaced by the lithium atom, leading to derivatives with the C-Li bond. The latter are highly reactive but unstable. However, the lithium atom in such unstable organometallics can be replaced with tin moiety, thus providing stable stannyl intermediates, which can be easily purified. Such a facile mutual exchangeability of the metal (Li→ ;Sn and vice versa) makes these sugar organometallics particularly attractive during stereocontrolled syntheses.In this review carbohydrate derivatives containing the metal atom (tin or lithium) placed at the sp³ carbon atom as well as at sp² and sp centers (at various positions of the sugar molecule) are reviewed. In addition, selected derivatives in which the metal is connected directly to the anomeric center are described.General methods of the synthesis of these important organometallic intermediates are evaluated. Application of lithiated or stannylated monosaccharide derivatives in the stereoselective syntheses is emphasized. The mechanistic aspects of these processes are discussed.

The aim of this review is to discuss the accomplishments made in the area of the stereoselective formation of a 1,2-cis glycosidic bond. Importance of this subject derives primarily from the natural occurrence of numerous 1,2-cis-linked oligosaccharides, glycosides, and glycoconjugates, which are widely distributed in living tissues. These compounds are also found in the human milk, in blood group compounds, in bacterial lipopolysaccharide antigens, and many other sources. A great number of reviews and book chapters dedicated to the oligosaccharide synthesis have recently emerged, and therefore general aspects of the glycosidic bond formation are discussed only up to a certain extent. Instead, this review is focused primarily on the glycosylation methods for the synthesis of 1,2-cis glycosides, which are traditionally underrepresented in the literature.

The molecular recognition of carbohydrates in water is an intriguing subject in view of the important role of saccharides in biological activities, such as intercellular recognition, signal transduction or as targets of bacterial / viral infection of cells. Considerable efforts have been directed toward understanding and mimicking such recognition processes, and developing effective agents to control these events. Driven by the need to create very efficient methods to combine a detectable signal with the recognition process, the past few years have seen a major push towards practically useful synthetic carbohydrate sensors.This review summarizes the recent achievements upon the preparation of synthetic receptors for carbohydrate recognition in water. Single molecule sensors based on boronic acids as well as polymeric receptors for saccharide sensing are discussed. Current research efforts are summarized, which address the development of operational sugar sensors for online monitoring and for long-term stability. Special emphasis is given to sugar sensing probes with a signal detection system, which is based on ligand exchange. The discussion in this review further includes polymeric carbohydrate receptors, which generate the sensing signal by altering the surrounding matrix property of the saccharide recognition site. Also, the recent developments to prepare carbohydrate recognition sites with high chiral discrimination ability are highlighted.